Automotive electronic control unit and data rewriting method for automotive electronic control unit

ABSTRACT

An automotive electronic control unit receives rewrite data wirelessly transmitted in units of a predetermined size from an external device and rewrites data stored in a nonvolatile memory based on the rewrite data. At this time, the rewrite data is communicated by switching between broadcast communication and unicast communication, or between multicast communication and unicast communication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for rewriting data on anin-vehicle electronic control unit.

2. Description of Related Art

In an in-vehicle electronic control unit, for example, data such asprograms and control parameters stored in a nonvolatile memory, such asan EEPROM (Electrically Erasable Programmable Read Only Memory) or aflash ROM (Read Only Memory), sometimes needs to be rewritten due tofunctional updating or the like. Therefore, as described in JapaneseLaid-Open (Kokai) Patent Application Publication No. 2010-19175, thereis proposed a technique in which rewrite data is transmitted wirelesslyfrom a rewriting tool to multiple vehicles to rewrite data on anelectronic control unit in each of the vehicles that received therewrite data.

Among vehicles of different specifications, only part of the datastructure in electronic control units may be different, such as a casein which control parameters are different but the program is the same inthe electronic control units. Since the conventional technique assumesthat the data structure is the same in electronic control units, data inelectronic control units having data structures different only in partcannot be rewritten concurrently. Therefore, data rewriting has to beperformed on each group of vehicles with electronic control units havinga same data structure, resulting in inefficient data rewriting.

SUMMARY OF THE INVENTION

An automotive electronic control unit receives rewrite data wirelesslytransmitted in units of a predetermined size from an external device,and rewrites data stored in a nonvolatile memory based on the rewritedata. At this time, the rewrite data is communicated by switchingbetween broadcast communication and unicast communication, and betweenmulticast communication and unicast communication.

Other objects and features of aspects of this invention will beunderstood from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating the outline of an example of a datarewriting system.

FIG. 2 is a flowchart illustrating an example of data rewriteprocessing.

FIG. 3 is a flowchart illustrating the example of data rewriteprocessing.

FIG. 4 is a flowchart illustrating the example of data rewriteprocessing.

FIG. 5 is a view illustrating a relationship between a communicablerange and target vehicles/non-target vehicles.

FIG. 6 is a view illustrating a relationship between overlapping ofcommunicable ranges and target vehicles.

FIG. 7 is a view describing preconditions in a specific example.

FIG. 8 is a view describing the outline of data rewrite processing inthe example.

DESCRIPTION OF EMBODIMENT

An embodiment for carrying out the present invention will now bedescribed in detail with reference to the accompanying drawings.

FIG. 1 illustrates an example of a data rewriting system for rewritingdata on an in-vehicle electronic control unit.

Plural electronic control units (ECUs) 102 for controlling an engine, anautomatic transmission, and the like are installed in a vehicle 100.Each electronic control unit 102 includes a microcomputer, in which aCPU (Central Processing Unit (processor)), a ROM, a RAM (Random AccessMemory), I/O (Input/Output), and the like are incorporated, and anonvolatile memory, such as an EEPROM or a flash ROM, capable ofrewriting data electrically. Electronic control unit 102 performsarithmetic processing on signals from various sensors according to aprogram stored in the nonvolatile memory to output an operation signalto the engine, the automatic transmission, or the like.

Vehicle 100 is also equipped with various electric parts, such as hazardlights 104 as exterior lights, a vehicle horn 106 as an alarm horn, andthe like. The various electric parts are controlled by a BCM (BodyControl Module) 108.

Furthermore, vehicle 100 is equipped with a transceiver 110 forperforming radio communication with external devices outside of thevehicle. Electronic control unit 102, BCM 108, and transceiver 110 areconnected in a manner to be communicable with one another through anin-car network 112 such as CAN (Controller Area Network).

A rewriting tool 200 is provided as an example of an external deviceoutside of the vehicle to perform radio communication with transceiver110 of vehicle 100. Rewriting tool 200 has a built-in transceiver 202for transmitting and receiving data by radio. Rewriting tool 200 is anapparatus including input and output devices such as a monitor andkeyboard, transceiver 202, and a microcomputer for controlling the inputand output devices, which can be made up with a notebook-size personalcomputer, for example.

When data on electronic control unit 102 of vehicle 100 is to berewritten, rewrite data is stored, for example, in a rewritable memoryof rewriting tool 200, and an operator manipulates rewriting tool 200accordingly to do the rewriting task. Note that rewriting tool 200 is anapparatus technically manipulated by an operator at a maintenancefactory or a dealer to rewrite data on electronic control unit 102 ofvehicle 100, which may be implemented by installing software on ageneral-purpose computer or as a dedicated apparatus.

Here, transceiver 110 of vehicle 100 and transceiver 202 of rewritingtool 200 can perform radio communication with each other while freelyswitching among broadcast communication, multicast communication, andunicast communication.

FIG. 2 to FIG. 4 illustrate an example of data rewrite processing forrewriting data on electronic control unit 102 installed in vehicle 100by using rewriting tool 200. The following description assumes thatmultiple vehicles 100 as data rewriting targets are packed together in amotor pool, a transport container, or the like to rewrite data on thesevehicles 100 concurrently. Note that vehicles 100 that are not datarewriting targets may be mixed in the motor pool, the transportcontainer, or the like.

Before starting the task, the operator turns on a key switch of each ofthe data rewriting target vehicles 100 to power on electronic controlunit 102, transceiver 110, and the like as a control system of vehicle100. This can exclude vehicles 100 that are not data rewriting targetsfrom data rewriting targets even when the vehicles 100 are mixed in aradio communicable range of rewriting tool 200.

When the operator starts an engine of vehicle 100 before starting thetask, the battery can be prevented from running out in the middle of thetask even if it takes a long time to do the data rewriting task. Thus,the fact that the engine is in operation can also be a precondition fordata rewriting. In this case, however, if the engine is automaticallystarted by a drop of battery voltage in a hybrid vehicle, the operatorwill have only to turn the key switch on.

Furthermore, while transceiver 110 of vehicle 100 is in a communicationstandby state in which power is always supplied, when it receives acommunication from rewriting tool 200, power supply to electroniccontrol unit 102 may be started or the engine may be automaticallystarted. In this case, the operator does not need to work on eachvehicle 100 individually, and this enables the operator to start therewriting task immediately, thereby enhancing the work efficiency.

Furthermore, transceiver 110 may be removable from vehicle 100. In thiscase, the operator has just to attach transceiver 110 to vehicle 100 asa data rewriting target to eliminate any problem even if vehicles 100that are not data rewriting targets are mixed in the motor pool or thelike.

Note that the embodiment may be applied to electric vehicles and thelike as well as vehicle 100 with an engine.

When such a preparatory process is completed, first, rewriting tool 200transmits a response command to multiple vehicles 100 in broadcastcommunication in which no radio communication partners are specified tosearch for vehicles 100 existing in a communicable range (step S100).The search for vehicles 100 is made in such a manner that the operatormanipulates rewriting tool 200 to order the start of the vehicle search.

When transceiver 110 of vehicle 100 receives the response command,transceiver 110 transmits, to rewriting tool 200, a response to theresponse command in unicast communication in which one radiocommunication partner is specified (step S200).

Here, rewriting tool 200 that received the response to the responsecommand may make the following determinations: When the level(intensity) of radio waves transmitted from vehicle 100 is equal to orgreater than a threshold, all vehicles 100 that meet such a conditionare specified as rewriting target candidates. On the other hand, whenthe level of radio waves transmitted from vehicle 100 is less than thethreshold even in a communicable state, rewriting tool 200 determinesthat reliable transmission and reception is difficult and hence isallowed to exclude the vehicle from the rewriting target candidates (seeFIG. 5). The threshold is preset as the minimum allowable value for thelevel of radio waves capable of transmitting and receiving data stably.This can avoid failing in data rewriting depending on the communicationstate, allowing rewriting tool 200 to carry out the data rewriting taskwithout fail.

Furthermore, when two or more rewriting tools 200 are arranged in adistributed manner and operated concurrently, there is a case in whichvehicles 100 exist in a region in which communicable ranges of two ormore rewriting tools 200 overlap. In this case, priority is given torewriting tool 200 first starting communication with a certain vehicle100, and when another rewriting tool 200 tries to communicate later,transceiver 110 of vehicle 100 may not make a response thereto andexchange data only with rewriting tool 200 first starting radiocommunication (see FIG. 6). Thus, when two or more rewriting tools 200are arranged in a distributed manner to carry out concurrent tasksbecause the number of vehicles 100 is too large, even if certain vehicle100 is located within communicable ranges of two or more rewriting tools200, one rewriting tool 200 can be identified as a communication partnerto transmit and receive data without fail.

Furthermore, when transceiver 110 of vehicle 100 receives signals fromtwo or more rewriting tools 200, it can identify, as the communicationpartner, rewriting tool 200 transmitting a signal highest in the levelof radio waves, i.e., nearest rewriting tool 200 can be identified asthe communication partner.

Rewriting tool 200 that received a response to the response command fromvehicle 100 requests, in broadcast communication, vehicle identificationinformation to vehicle 100 that made the response (step S101).

Transceiver 110 of vehicle 100 that received the request for vehicleidentification information returns vehicle identification information torewriting tool 200 in unicast communication (step S202). The vehicleidentification information may be a single piece of information, such asthe vehicle license number, the vehicle identification number, the typeof vehicle, or the data structure of electronic control unit 102, or acombination of plural pieces of information. The vehicle identificationinformation may be prestored for each vehicle 100, for example, intransceiver 110 or electronic control unit 102.

Rewriting tool 200 that received the vehicle identification informationidentifies vehicles 100 as data rewriting targets based on the vehicleidentification information (step S102). Specifically, the operator usesa keyboard and the like to enter information on data rewriting targetvehicles in advance into rewriting tool 200. Then, rewriting tool 200compares the information on data rewriting target vehicles with vehicleidentification information sent from vehicles 100 to identify vehicles100 as as data rewriting targets. In other words, the consistencybetween the rewrite data and the vehicle identification information(vehicle information) is checked, and when they are consistent, thecommunication of the rewrite data is started in a manner to be describedlater. Thus, although vehicles 100 that are not data rewriting targetsmay be mixed in the vehicles 100 searched for in step S100, since therewriting target candidates are narrowed down based on the vehicleidentification information to exclude the vehicles 100 from datarewriting targets, no problem arises.

For example, when rewrite data is downloaded from a host computer,rewriting tool 200 may also download together information on datarewriting target vehicles to which the rewrite data is applied.Furthermore, information on data rewriting target vehicles may also beintegrally attached to the rewrite data.

When identifying data rewriting target vehicles, rewriting tool 200 maytransmit information indicative of being identified as the targetvehicles to each vehicle 100, so that transceiver 110 of vehicle 100that received this information instructs BCM 108 to put hazard lights104 on, actuate vehicle horn 106, or the like. Thus, the operator caneasily identify vehicle 100 specified as a target vehicle from amongmultiple vehicles 100 placed side by side in the motor pool. Forexample, the operator becomes aware of vehicle 100 with which rewritingtool 200 did not communicate because the operator forgot to turn the keyswitch on despite the fact that vehicle 100 should have been a targetvehicle, allowing the operator to turn the key switch on anew.

Instead of hazard lights 104, other exterior lights such as headlights,rear lights, or brake lights can be put on, and instead of vehicle horn106, the alarm of an antitheft device can be actuated. Furthermore,instead of flashing lights or sound to make the operator become aware ofa target vehicle, the movement of vehicle parts can make the operatorbecome aware of the target vehicle. Specifically, wipers can be actuatedor an automatic opening and closing device can be used to open or closea door or a window to make the operator identify, as a state change ofan individual vehicle, vehicle 100 selected as a target vehicle.

Here, various exterior lights including hazard lights 104, vehicle horn106, the antitheft device, the wipers, and the automatic opening andclosing device are all electric parts, but the electric parts to beactuated are not limited thereto.

Rewriting tool 200 that identified data rewriting target vehiclesrequests a seed value for encryption to the target vehicles throughbroadcast communication or multicast communication in the case ofidentifying multiple communication partners so as to ensure the securityof communication (step S103). Here, broadcast communication is used whenall vehicles 100 searched for are target vehicles, and multicastcommunication is used when vehicle(s) 100 that is not a targetvehicle(s) is included in the vehicles 100 searched for.

Transceiver 110 of vehicle 100 that received the request for a seedvalue generates a seed value using a random number (step S203).

Transceiver 110 of vehicle 100 that generated the seed value returns thegenerated seed value to rewriting tool 200 in unicast communication(step S204).

Furthermore, transceiver 110 of vehicle 100 generates an encryption keyfrom the generated seed value and stores the encryption key (step S205).

Rewriting tool 200 that received the seed value generates an encryptionkey from the seed value in the same manner as transceiver 110 of vehicle100 to encrypt a predetermined common key (step S104). Here, since theencryption key is generated in the same manner as that of transceiver110 of vehicle 100, vehicle 100 and rewriting tool 200 can share theencryption key. Then, rewriting tool 200 transmits the encrypted commonkey to the target vehicles in broadcast communication or multicastcommunication (step S105).

Transceiver 110 of vehicle 100 that received the common key decrypts thecommon key using the encryption key (step S206). Then, transceiver 110of vehicle 100 returns, to rewriting tool 200, a response in unicastcommunication to indicate that the common key is able to be decrypted(step S207).

After decrypting the common key, transceiver 110 may deliver this commonkey to each electronic control unit 102. This enables each electroniccontrol unit 102 to decrypt encrypted data. Furthermore, the common keymay be decrypted by each electronic control unit 102, rather than bytransceiver 110.

Rewriting tool 200 that received the response indicating that the commonkey is able to be decrypted makes a request to the target vehicles formemory erasure through broadcast communication or multicastcommunication (step S106). Included in the request for memory erasureare information for identifying electronic control unit 102, informationfor specifying an erasure range in the nonvolatile memory of electroniccontrol unit 102, and the like. These pieces of information may bespecified, for example, from information on data rewriting targetvehicles entered by the operator. Note that the memory erasure isprocessing performed prior to data rewriting.

Transceiver 110 of vehicle 100 that received the memory erasure requestidentifies at least one electronic control unit 102, which is subjectedto memory erasure, based on the information included in the request, andtransfers, to the electronic control unit 102, the memory erasurerequest including the information for specifying the erasure range.Then, electronic control unit 102 that received the memory erasurerequest erases the memory in the erasure range (step S208). Uponcompletion of the memory erasure, electronic control unit 102 returns aresponse indicative of completion of the memory erasure to rewritingtool 200 through transceiver 110 in unicast communication (step S209).Note that electronic control unit 102 and rewriting tool 200 may checkwith each other regarding the progress status of the memory erasure.

On the other hand, rewriting tool 200 waits until responses includingcompletion of memory erasure are returned from all the target vehicles(step S107).

Furthermore, rewriting tool 200 sequentially reads fragmented pieces ofrewrite data stored in the memory in units of a predetermined size(e.g., 128 bytes) (step S108) to encrypt the predetermined size ofrewrite data using the common key (step S109). After that, for example,rewriting tool 200 refers to the information on data rewriting targetvehicles to determine whether the encrypted rewrite data is same data tothe target vehicles (step S110). Then, when determining that it is samedata to the target vehicles, rewriting tool 200 transmits the encryptedrewrite data to vehicles 100 in broadcast communication or multicastcommunication (step S111). On the other hand, when determining that itis not same data to the target vehicles, i.e., that it is unique dataspecific to each vehicle 100, rewriting tool 200 transmits, in unicastcommunication, the encrypted rewrite data to vehicle 100 to which theunique data is to be applied (step S112).

Transceiver 110 of vehicle 100 that received the rewrite dataidentifies, based on information included in the rewrite data,electronic control unit 102 to which the rewrite data is applied, andtransfers the rewrite data to the electronic control unit 102.Electronic control unit 102 that received the rewrite data decrypts therewrite data using the common key (step S210) and writes the rewritedata sequentially into an area to which the rewrite data is applied(step S211). Upon completion of writing the rewrite data, electroniccontrol unit 102 returns a response indicative of completion of datawriting to rewriting tool 200 through transceiver 110 in unicastcommunication (step S212).

Here, when electronic control unit 102 of vehicle 100 has not receivedrewrite data from rewriting tool 200 for a predetermined time, the datarewrite processing may be stopped. In this case, for example, when aradio disturbance occurs, since the data rewrite processing is stopped,such a situation that the data rewrite processing is never ended can beavoided.

Rewriting tool 200 that received the response indicative of completionof data writing determines, for example, whether the last piece ofrewrite data stored in the memory is processed to determine whether therewriting task is completed (step S113). Then, when determining that therewriting task is completed, rewriting tool 200 ends the task, whilewhen determining that the rewriting task is not completed, theprocessing starting from step S108 is repeated.

When the rewriting task is completed, electronic control unit 102 ofvehicle 100 determines whether data is rewritten normally, and accordingto the determination result, it may instruct BCM 108 to actuate electricparts. This enables the operator to distinguish vehicles 100 with datarewriting performed normally from vehicles 100 failing in data rewritingamong vehicles 100 placed side by side in the motor pool or the like.

Vehicle 100 failing in data rewriting may be notified to rewriting tool200, so that rewriting tool 200 performs data rewrite processing againthrough unicast communication. In this case, the repetition of datarewrite processing may be limited to a given number of times or fewer,and when rewriting is not completed normally after the data rewriteprocessing is repeated the given number of times, the data rewriteprocessing is stopped to make rewriting tool 200 display that vehicle100 concerned is unable to rewrite data. This allows the operatormanipulating rewriting tool 200 to become aware of vehicle 100 failingin data rewriting. Note that since there is a possibility that datarewrite processing has failed due to radio interference, rewriting tool200 and vehicle 100 may be connected by cable to perform data rewritingagain.

According to this data rewriting system, rewriting tool 200 searches forvehicles 100 through broadcast communication to make a request to thevehicles 100 for vehicle identification information. After that, basedon vehicle identification information, the rewriting tool 200 identifiesvehicles 100 as data rewriting targets from among vehicles 100 searchedfor, and generates a common key for communicating with the vehicles 100to be transmitted. Furthermore, rewriting tool 200 makes a request tovehicles 100 as the data rewriting targets for memory erasure in a datarewriting area, and waits for responses from all vehicles 100 as thedata rewriting targets. Then, rewriting tool 200 uses the common key toencrypt rewrite data divided by predetermined size, and sequentiallytransmits the rewrite data in synchronization with vehicle 100 to ensurethe communication of the rewrite data. At this time, when the rewritedata is the same data in all vehicles 100 as the data rewriting targets,rewriting tool 200 transmits the encrypted rewrite data in broadcastcommunication or multicast communication, whereas when it is unique dataspecific to each vehicle 100 as a data rewriting target, rewriting tool200 transmits the encrypted rewrite data in unicast communication.

On the other hand, when receiving the memory erasure request fromrewriting tool 200, vehicle 100 erases the memory based on informationfor specifying the erasure range included in the request. Furthermore,when receiving rewrite data from rewriting tool 200, vehicle 100decrypts the rewrite data using the common key to rewrite data in anarea to which the rewrite data is to be applied.

Thus, same data to multiple vehicles 100 are rewritten through broadcastcommunication or multicast communication, while unique data specific toeach vehicle 100 is rewritten through unicast communication. Therefore,even when the capacity of the nonvolatile memory in which the data isrewritten is increased in electronic control unit 102 of vehicle 100,since data rewriting of same data is performed in parallel throughbroadcast communication or multicast communication, data rewritingefficiency can be enhanced. Although data rewriting of unique data isperformed through unicast communication, when unique data in the datastructure of electronic control unit 102 is only a small portion, suchas the same vehicle model or the same series of vehicle type, datarewriting efficiency is not so degraded. Since such an effect is exertedmore greatly as the number of vehicles 100 that are data rewritingtargets increases, this will be particularly valuable to automobilemanufacturers that perform data rewriting on a very large number ofvehicles 100.

While data rewriting is being performed on a nonvolatile memory inelectronic control unit 102 of vehicle 100, this electronic control unitcannot communicate with another electronic control unit 102, and henceabnormality information detected by an abnormality diagnosis function isaccumulated. In this case, rewriting tool 200 may transmit, in unicastcommunication, a command for erasing abnormality information to vehicle100 in which data rewriting is completed normally. This enableselectronic control unit 102 of vehicle 100 to erase abnormalityinformation accumulated during data rewriting in response to the commandtransmitted from rewriting tool 200.

Note that various processing performed by transceiver 110 of vehicle 100in the aforementioned embodiment may be performed by each electroniccontrol unit 102 installed in the vehicle 100. In this case, transceiver110 has only the function of transmitting and receiving data, commands,and the like to and from rewriting tool 200.

A specific example will be described for the sake of facilitatingunderstanding of the aforementioned embodiment.

FIG. 7 illustrates a specific example in which rewriting tool 200rewrites data on three vehicles 100 (vehicle 1 to vehicle 3) packedtogether in a motor pool. It is assumed that the data structures inelectronic control units 102 of vehicle 1 to vehicle 3 consist of samedata A and C, and unique data B1 to B3 as shown in FIG. 7. Note that thefollowing description will be made of only main processing and otherprocessing such as that for ensuring security will be omitted.

As shown in FIG. 8, rewriting tool 200 transmits a response command inbroadcast communication to search for vehicles 100 existing in the motorpool. Vehicle 1 to vehicle 3 that received the response command make aresponse through unicast communication. Rewriting tool 200 that receivedthis response makes a request to vehicle 1 to vehicle 3 for vehicleidentification information through broadcast communication. Vehicle 1 tovehicle 3 that received the request for vehicle identificationinformation return vehicle identification information in unicastcommunication. After that, rewriting tool 200 makes a request to vehicle1 to vehicle 3 for memory erasure through broadcast communication.Vehicle 1 to vehicle 3 that received the request for memory erasureerase the memory in a predetermined area of electronic control unit 102,and return a response indicative of completion of the memory erasure inunicast communication.

Rewriting tool 200 analyzes the data structures of vehicle 1 to vehicle3, and first transmits same data A to vehicle 1 to vehicle 3 inbroadcast communication. Vehicle 1 to vehicle 3 that received same dataA rewrite data on electronic control unit 102 based on same data A, andmake a response in unicast communication. Rewriting tool 200 thatreceived this response transmits unique data B1 to vehicle 1 in unicastcommunication because data following same data A in vehicle 1 to vehicle3 are unique data. Vehicle 1 that received unique data B1 rewrites datain electronic control unit 102 based on unique data B1, and makes aresponse in unicast communication. Rewriting tool 200 also transmitsunique data B2 to vehicle 2 in unicast communication, and vehicle 2 thatreceived this rewrites data in electronic control unit 102, and makes aresponse in unicast communication. Furthermore, rewriting tool 200transmits unique data B3 to vehicle 3 in unicast communication, andvehicle 3 that received this rewrites data in electronic control unit102 and makes a response in unicast communication.

After that, since data following unique data B1 to B3 in vehicle 1 tovehicle 3 is same data C, rewriting tool 200 transmits same data C tovehicle 1 to vehicle 3 in broadcast communication. Vehicle 1 to vehicle3 that received same data C rewrite data in electronic control unit 102based on same data C, and make a response in unicast communication.

Thus, according to this example, since same data A and C in electroniccontrol unit 102 of vehicle 1 to vehicle 3 are rewritten in parallelthrough broadcast communication, it will be understood that datarewriting efficiency is enhanced.

The entire contents of Japanese Patent Application No. 2012-063833,filed Mar. 21, 2012, are incorporated herein by reference.

While only a select embodiment has been chosen to illustrate the presentinvention, it will be apparent to those skilled in the art from thisdisclosure that various changes and modifications can be made hereinwithout departing from the scope of the invention as defined in theappended claims.

Furthermore, the foregoing descriptions of the embodiments according tothe present invention are provided for illustration only, and not forthe purpose of limiting the invention, the invention as claimed in theappended claims and their equivalents.

What is claimed is:
 1. An automotive electronic control unit comprising:a nonvolatile memory which stores data; and a processor which receivesrewrite data wirelessly transmitted in units of a predetermined sizefrom an external device by switching between broadcast communication andunicast communication, or between multicast communication and unicastcommunication, and rewrites data stored in the nonvolatile memory basedon the rewrite data.
 2. The automotive electronic control unit accordingto claim 1, wherein a same portion of the rewrite data to a plurality ofautomobiles is communicated in broadcast communication or multicastcommunication and a unique portion of the rewrite data specific to eachautomobile is communicated in unicast communication.
 3. The automotiveelectronic control unit according to claim 1, wherein consistencybetween the rewrite data and vehicle information is checked, and whenthe rewrite data and the vehicle information are consistent,communication of the rewrite data is started.
 4. The automotiveelectronic control unit according to claim 1, wherein the rewrite datais communicated to an automobile identified by vehicle information. 5.The automotive electronic control unit according to claim 1, wherein theautomotive electronic control unit is powered on before data isrewritten.
 6. The automotive electronic control unit according to claim1, wherein the rewrite data is communicated after being encrypted by acommon key shared with the external device.
 7. The automotive electroniccontrol unit according to claim 1, wherein the rewrite data iscommunicated in synchronization with the external device.
 8. Theautomotive electronic control unit according to claim 1, wherein whendata rewrite processing fails, data stored in the nonvolatile memory isrewritten based on the rewrite data communicated in unicastcommunication.
 9. The automotive electronic control unit according toclaim 1, wherein when the data rewrite processing fails, the externaldevice is notified of the failure.
 10. The automotive electronic controlunit according to claim 1, wherein when the rewriting of data isnormally completed, abnormality information is erased in response to acommand communicated in unicast communication.
 11. A data rewritingmethod for an automotive electronic control unit having a nonvolatilememory, comprising the steps of: receiving rewrite data wirelesslytransmitted in units of a predetermined size from an external device byswitching between broadcast communication and unicast communication, orbetween multicast communication and unicast communication; and rewritingdata stored in the nonvolatile memory based on the rewrite data.
 12. Thedata rewriting method for an automotive electronic control unitaccording to claim 11, wherein a same portion of the rewrite data to aplurality of automobiles is communicated in broadcast communication ormulticast communication and a unique portion of the rewrite dataspecific to each automobile is communicated in unicast communication.13. The data rewriting method for an automotive electronic control unitaccording to claim 11, wherein consistency between the rewrite data andvehicle information is checked, and when the rewrite data and thevehicle information are consistent, communication of the rewrite data isstarted.
 14. The data rewriting method for an automotive electroniccontrol unit according to claim 11, wherein the rewrite data iscommunicated to an automobile identified by vehicle information.
 15. Thedata rewriting method for an automotive electronic control unitaccording to claim 11, wherein the automotive electronic control unit ispowered on before data is rewritten.
 16. The data rewriting method foran automotive electronic control unit according to claim 11, wherein therewrite data is communicated after being encrypted by a common keyshared with the external device.
 17. The data rewriting method for anautomotive electronic control unit according to claim 11, wherein therewrite data is communicated in synchronization with the externaldevice.
 18. The data rewriting method for an automotive electroniccontrol unit according to claim 11, wherein when data rewrite processingfails, the automotive electronic control unit rewrites data stored inthe nonvolatile memory based on the rewrite data communicated in unicastcommunication.
 19. The data rewriting method for an automotiveelectronic control unit according to claim 11, wherein when the datarewrite processing fails, the automotive electronic control unitnotifies the external device of the failure.
 20. The data rewritingmethod for an automotive electronic control unit according to claim 11,wherein when the rewriting of data is normally completed, the automotiveelectronic control unit erases abnormality information in response to acommand communicated in unicast communication.